Water-dispersed coating composition of short oil alkyd resin and alkanolamine

ABSTRACT

A water-dispersed coating composition of a short oil alkyd resin and an alkanolamine represented by the formula   &lt;IMAGE&gt;   where R is hydrogen, methyl, ethyl or hydroxymethyl.

BACKGROUND OF THE INVENTION

This invention relates to a resin composition. In a particular aspect, this invention relates to an alkyd resin composition having improved flexibility.

Alkyd resins, i.e. the reaction product of a polyol with a mixture of a polybasic acid and a monobasic acid, are widely used in baked coatings. The resins so used are only partially polymerized, dissolved in a suitable solvent, a catalyst is added and whatever pigmentation is desired and then applied to the article to be coated. The article is then heated or baked at an elevated temperature to cure the resin, i.e. to complete the polymerization. Alkyd resins are very successful in coatings of this type. If the amount of monobasic acid, e.g. a fatty acid is large, the coating is very flexible, but unduly soft and easily scratched. However, if the amount of monobasic acid is relatively small, the resin suffers from the disadvantage of being very hard and lacking flexibility. Accordingly there is a need to improve the flexibility of alkyl resin coatings without undue loss of hardness of such coatings.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a resin composition.

It is another object of this invention to provide a resin composition having improved flexibility.

Other objects of this invention will be apparent to those skilled in the art from the disclosure herein.

It is the discovery of the present invention to provide a water-dispersed composition consisting essentially of an amine-neutralized short-oil alkyd resin having a high acid number and from 15% to 40% by weight based on the alkyd resin of an alkanolamine represented by the formula ##STR2## where R is hydrogen, methyl, ethyl or hydroxymethyl. The alkanolamine acts as a cross-linking agent and improves the flexibility of the short oil alkyd without loss of hardness.

DETAILED DESCRIPTION

It is contemplated that the composition of the present invention will be in the form of a water-based coating which is applied to an article to be coated by any convenient means, e.g. by brushing, dipping, spraying, or electrostatic spraying, all of which methods are well known in the art. The formulation of such coatings is also well-known in the art. In general, a short-oil alkyd resin having a high acid number, e.g. of about 35 to 65, is neutralized with ammonia, an alkyl amine, such as morpholine, or an alkanolamine whereupon it becomes water-soluble. The solution thereby obtained can be used, without additional components, but usually it is preferred to add a modifier, e.g. a phenol-formaldehyde or urea-formaldehyde resin, a metallic drying catalyst, and color agent such as a pigment or dye. It is contemplated that any of the formulations known in the art can be used in the practice of the present invention, since the invention is directed to the use of the alkanolamine in such formulations.

In general, an alkyd resin is the product obtained by reacting a mixture of dibasic and/or tribasic acids and a monobasic acid with polyol. Typical polybasic acids include the phthalic acids and phthalic anhydride, maleic anhydride, fumaric acid and trimellitic anhydride. Typical polyols include ethylene glycol and diethylene glycol, glycerol, trimethylolethane, trimethylolpropane, mono-, di- and tri-pentaerythritols and sorbitol. The degree of polymerization is controlled by the reaction and is indicated by the acid number, a high acid number being indicative of free carboxyl groups which usually indicate incomplete polymerization.

A fatty acid, usually an unsaturated one such as linoleic or linolenic, is usually included to provide flexibility in the finished resin. Alkanolamines are known to react with carboxylic acids to form oxazolines and tris (hydroxymethyl) aminomethane has been used as the polyol in alkyd resin synthesis. However alkanolamines have not previously been known to be useful as cross-linking agents and flexibility improvers.

Either the free fatty acid or sources thereof are used in the reaction mixture. Typical sources of fatty acids include natural oils such as linseed, soybean, safflower, tall, fish, tung, oiticica, castor, dehydrated castor, coconut, and cottonseed. Also lauric, pelargonic, isodecanoic and isooctanoic acids are used in minor amounts as substitutes for part of the fatty acids to terminate the polymer or modify the properties of the resin. Commonly used non-fatty, mono-basic acids include benzoic, butyl benzoic and dimethylolpropionic acids. Other modifiers include resins such as rosin, phenol-formaldehyde, urea-formaldehyde, styrene, alpha methyl styrene, vinyl toluene, acrylic esters and silicone intermediates, as is well-known in the art.

Depending on the amount of fatty acid present, the resin is denoted as a short oil, medium oil or long oil length alkyd. The short oil resins are typically hard and rather brittle, whereas the long oil resins are flexible but lack hardness. A resin having from about 33-48% - or even as low as 25% - oil is generally known as a short oil alkyd. The range of 43-48 is sometimes referred to as a short medium oil alkyd. No. sharp line of demarcation between these categories is recognized in the art.

The water-based coating of the present invention can be formulated with any of the short oil alkyd resins, e.g. of from about 25 to 48% oil length, having a high acid number of 35-65, or even above, although an oil length of from 33 to 43% is preferred. The alkyd is neutralized in the presence of water with a suitable neutralizing agent, many of which are known in the art, e.g. ammonia, morpholine, mono-di- or triethanolamine, the isopropanolamines, 2-amino-2-methyl-1-propanol, the ethylamines, the propylamines, etc., or mixtures thereof, whereupon it becomes water-soluble. The solubilized resin is then diluted with sufficient water to yield a desired viscosity and solids content. Typically the water content of the finished formulation will be in the range of 35-45% by weight. From about 15% to about 40% of an alkanolamine represented by formula I, based on the weight of the alkyd resin, is then incorporated in the formulation. Any of the catalysts, pigments, dyes, modifying resins or other additives known in the art can also be added as desired. When used, the coating should be baked at a temperature of, for example, 120° to about 150° C.

The alkanolamines suitable for the practice of this invention include but are not limited to 2-amino-1,3-propanediol; 2-amino-2-methyl-1,3-propanediol; 2-amino-2-ethyl-1,3-propanediol; and preferably tris (hydroxymethyl)-aminomethane. All of these alkanolamines are known in the art and, except for the first one where R is hydrogen, are commercially available. The commercial products are suitable for the practice of this invention. They can also be readily prepared by the catalytic hydrogenation of the corresponding nitro compounds.

The invention will be better understood with reference to the following examples. It is understood however, that the examples are intended only to illustrate the invention and it is not intended that the invention be limited thereby.

EXAMPLE 1

A commercially-available, water-soluble type short oil alkyd resin was formulated into a typical water-based coating. The resin used was Aquamac 1085, manufactured by the Resin Division, IMC Chemical Group, Inc., Carpentersville, Illinois 60110. This resin is prepared by reacting the following ingredients

    ______________________________________                                         *Unsaturated tall oil fatty acid                                                                        31.2 parts                                            Benzoic acid             1.7                                                   Trimethylolethane        29.4                                                  Isophthalic acid         29.4                                                  Trimellitic anhydride    8.3                                                   ______________________________________                                          *Pamolyn 200 marketed by Hercules, Inc.                                  

The resulting product had an oil length of about 33% and acid value of 50-60. It was dissolved in a mixture of butoxyethanol and isobutyl alcohol in a 2:1 by volume ratio to provide a solids content of about 70% by weight.

The formula for the water based coating was as follows:

    ______________________________________                                         Alkyd resin (70% solids basis)                                                                            26.5g                                               Triethylamine              2.2                                                 Water                      40.0                                                Metallic drier (6% Mn)     0.1                                                 Butoxyethanol              7.2                                                 Methylated urea-formaldehyde resin                                                                        12.5                                                p-nitrotoluene sulfonic acid                                                                              1.0                                                 Total                      89.5                                                ______________________________________                                    

The above formulation was duplicated except that 2.84 g of tris (hydroxymethyl) aminomethane-hereinafter referred to as TA - was added, equal to 15.3% based on the weight of the alkyd. Each formulation was used to coat two steel panels with a 3 mil wet film. There were then baked for 15 minutes at 120° and 150° C respectively. The panels were tested for flexibility by reverse impact and mandrel bend and for hardness. The results are given in table 1. They show that the TA contributes superior flexibility with only insignificant loss of hardness.

EXAMPLES 2-4

The experiment of example 1 was repeated in all essential details except that the amount of TA added was 4.27, 5.69 and 7.11 g respectively, equivalent to about 23, 30 and 38% respectively, based on the dry weight of the alkyd resin. The results are given in table 1.

                  TABLE 1                                                          ______________________________________                                                    Reverse                                                                        Impact,  Pencil    Mandrel                                                     inches/lb                                                                               Hardness  Bend, inches                                     ______________________________________                                         Control at                                                                              120°                                                                            20         4H      1/8                                                 150     12         5H       5/16                                      Example 1,                                                                              120°                                                                            55         4H      1/8                                                 150     32         5H      1/4                                        Example 2,                                                                              120°                                                                            20         3H      1/8                                                 150     78         4H      1/8                                        Example 3,                                                                              120°                                                                            78         2H      1/8                                                 150     60         4H      1/8                                        Example 4,                                                                              120°                                                                            78          B      1/8                                                 150     78         4H      1/8                                        ______________________________________                                    

It was concluded that the use of TA gives excellent results. Alkyds containing it possess superior flexibility as manifested by the improvement in the reverse impact test with no significant loss of hardness.

EXAMPLES 5-18

The experiment of example 1 is repeated in all essential details except that the alkyd resin is prepared from different polyols and acids. The polyols, polybasic acids and fatty acids, used are listed in the following table 2. The ratios thereof, and the reaction times are selected by known methods to provide the oil lengths and the acid members listed. The TA significantly improves the flexibility of coatings prepared from the alkyd resins with only minor effect on the hardness.

                                      TABLE 2                                      __________________________________________________________________________     Example                                    Oil  Acid                           Number                                                                                Polyol     Dibasic Acid                                                                               Fatty Acid or Oil                                                                           Length                                                                              Number                         __________________________________________________________________________     5    Ethylene glycol                                                                            Phthalic Anhydride                                                                          linseed oil  33   35                             6    Diethylene glycol                                                                          Terephthalic Acid                                                                           soybean oil  43   45                             7    Glycerol    Maleic Anhydride                                                                            safflower oil                                                                               45   41                             8    Trimethylol propane                                                                        Fumaric acid fish oil     35   37                             9    Pentaerythritol                                                                            Phthalic anhydride                                                                          tung oil     38   48                             10   Dipentaerythritol                                                                          Isophthalic acid                                                                            oiticica oil 44   52                             11   Tripentaerythritol                                                                         Trimellitic anhydride                                                                       castor oil   46   46                             12   Trimethylolethane                                                                          Maleic anhydride                                                                            dehydrated castor oil                                                                       34   56                             13   Glycerol    Fumaric acid coconut oil  37   39                             14   Ethylene glycol                                                                            Phthalic anhydride                                                                          cottonseed oil                                                                              35   60                             15   Pentaerythritol                                                                            Phthalic anhydride                                                                          lauric acid  40   44                             16   Diethyleneglycol                                                                           Phthalic anhydride                                                                          pelorgonic acid                                                                             41   65                             17   Dipentaerythritol                                                                          Phthalic anhydride                                                                          isodecanoic acid                                                                            34   38                             18   Trimethylolpropane                                                                         Phthalic anhydride                                                                          isooctanoic acid                                                                            45   43                             __________________________________________________________________________

EXAMPLE 19

The experiment of example 1 is repeated in all essential details except that 2-amino-1,3-propanediol is substituted for TA and the panels are baked at 150° C. The coatings thereby obtained exhibit greater flexibility without significant loss of hardness by comparison with a control coating.

EXAMPLE 20

The experiment of example 1 is repeated in all essential details except that 2-amino-2-methyl-1,3-propanediol is substituted for TA and the panels are baked at 150° C. The coatings thereby obtained exhibit greater flexibility without significant loss of hardness by comparison with a control coating.

EXAMPLE 21

The experiment of example 1 is repeated in all essential details except that 2-amino-2-ethyl-1,3-propanediol is substituted for TA and the panels are baked at 150° C. The coatings thereby obtained exhibit greater flexibility without significant loss of hardness by comparison with a control coating. 

I claim:
 1. A water dispersed coating composition consisting essentially of a mixture of an amine-neutralized short oil alkyd resin and an alkanolamine represented by the formula ##STR3## where R is hydrogen, methyl, ethyl or hydroxymethyl in a concentration of 15% to about 40% by weight of the alkyd resin.
 2. The composition of claim 1 wherein the alkyd resin has an oil length of from about 33 to
 48. 3. The composition of claim 1 wherein the alkyd resin has an acid number of from about 35 to about
 48. 4. The composition of claim 1 wherein the alkanolamine is present in an amount of 15% based on the weight of the resin.
 5. The composition of claim 1 wherein the alkanolamine is present in an amount of about 23%.
 6. The composition of claim 1 wherein the alkanolamine is present in an amount of about 30%.
 7. The composition of claim 1 wherein the alkanolamine is present in an amount of about 40%.
 8. The composition of claim 1 wherein the alkanolamine is 2-amino-1,3-propanediol.
 9. The composition of claim 1 wherein the alkanolamine is 2-amino-2-methyl-1,3-propanediol.
 10. The composition of claim 1 wherein the alkanolamine is 2-amino-2-ethyl-1,3-propanediol.
 11. The composition of claim 1 where the alkanolamine is Tris(hydroxymethyl)aminomethane. 